Nonmicrophonic tube



Patented Jan.2, 1945 NONMICROPHONIO TUBE Percy L. Spencer, West Newton, Mass. assiznor,

by mesne ass nts, to Baythcon Manufacturlng Company, Newton, Mass., a corporation of Delaware Application July 20, 1940, Serial No. 346,554

2. Claims. (Cl. 250-275) This invention relates to an electrical space discharge tube of the vacuum type in which the dimensions of the tube are reduced to relatively small values. In such a tube the problem of supporting the various tube elements and more particularly the filamentary cathode, so as to avoid vibration and consequent microphonic distortion in the output of the tube, is particularly acute.

.An object of this invention is to support the elements in such a tube so as to avoid vibration and microphonic distortion.

Another object is to simplify the assembly and manufacture of tubes of small size.

The foregoing and other objects will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein:

Fig. l is a cross-section of my novel tube taken along line l-l of Fig. 3;

Fig; 2 is a right-hand view of the electrode assembly shown in Fig. 1 with the glass envelope shown in cross-section;

Fig. 3 is a cross-sectional view of the electrode assembly taken along line 3-3 of Fig. 1; and

Fig. 4 is a skeleton view of the filament-supporting structure.

The tube illustrated contains an electrode assembly consisting of an anode l, a filamentary cathode 2, and a plurality of grids 3, 4 and 5. The grids are wound upon and supported by grid side rods 6, 1 and 8, respectively. Proper spacing and support of the electrodes are provided by upper and lower insulating spacers 9, preferably of mica. The spacers 9 are cut away to provide resilient projections l which are adapted to resiliently engage the inner Walls of the glass envelope. The spacers 9 are each provided with a triangular slot it having a rectangular recess in the base thereof in order to receive and support one of the side rods 6 of the grid 3.

The filamentary cathode 2 is retained in the apex of each of the triangular slots II. In order to support the lower end of the filamentary oathode 2, a U-bracket I3 is secured to the lower spacer 9 and projects from the lower side thereof. The bracket I3 has welded thereto a tab H which in turn is welded to the lower end of the filamentary cathode 2, and serves as a mechanical support and electrical connector therefor. A conducting spring member I is welded at one end to the upper end of the filamentary cathode 2, and at its other end to one of the side rods 8 of the grid 5. The spring l5 pulls upwardly on the filamentary cathode 2, and maintains the proper tension thereon. Furthermore, said spring projects beyond the apex of the upper triangular slot II so as to force the upper end of the filamentary cathode into the apex of said triangular slot. Likewise the tab it is located beyond the apex of the lower triangular slot ll so as to maintain the lower end of the filamentary cathode in said apex.

The anode I is provided with a plurality of tabs l6 at itsupper edge and a plurality of tabs H at its lower edge.- These tabs are bent over onto the upper and lower surfaces of the upper and lower spacers 9, respectively, and serve to maintain the electrode assembly in its assembled form, whereby it may be readily handled as a unit before insertion into the glass envelope. As an additional means for retaining the grid 5 in place within the electrode assembly, one of the side rods 8 may be provided with stops l8 welded to the upper and lower ends of said side rod and bearing against the upper and lower faces of the upper and lower spacers 9, respectively.

In order to provide for an external electrical connection to the anode I, a connector I9 is welded to one of the lower tabs l1 and also to a. lead-in conductor 20. Lead-in conductors 2t, 22, 23 and 24 are also provided for the electrodes 2, 3, 4 and 5, respectively. For this purpose the lead-in 2| is welded to the bracket 13, the leadin 22 is welded to one of the side rods 5, the leadin 23 is welded to one of the side rods. 1, and the lead-in 24 is welded to one of the side rods 8. A

ring 25 of getter material may be conveniently supported on the electrode assembly by being welded to the upper end of one of the side rods 8.

An electrode assembly, as described above, is compact and may readily be assembled as a unit so that it may later be inserted into the glass envelope. However, in such a structure, particularly in the relatively small sizes in which the applicant has incorporated it, a tendency exists for the filamentary cathode stretched between the spring l5 and the tab 14, to vibrate and introduce microphonic distortions in the output of the tube. In order to eliminate this difliculty, a spring wire 26 is provided. One end of this spring wire is welded to a tongue 21 formed in the side wall of the anode l by cutting a U-shaped slot therein. The spring wire 26, except for the point at which it is welded to the tongue 21, is covered with an insulating coating 28. When the tube is first assembled with the wire 26 welded to the tongue 21, the tongue 21 is initially located so that the spring wire 25 together with its insulating coating 28 is not in contact with the filamentary cathode 2, but lies to the left thereof in Figs. 2 and 4. When the assembly has been completed, a. pair of tweezers is used to bend the tongue 2! inwardly, which moves the coated end of the spring wire it against the filamentary cathode 2. By adjusting the degree of bending of th tongue 27, the proper tension can be placed upon the filamentary cathode 2 so as to avoid all objectionable vibration thereof. Any tendency for vibration to occur is absorbed by the spring wire 26 and the insulating coating 28 thereon.

When the above adjustment has been made, the electrode assembly is inserted as a unit within a straight-sided glass tube 28. The lower end of this tube is heated and softened sufficiently so that it may be pressed to make the press or seal 38. The upper end of the tube 29 is provided with th usual tubulation, exhausted and sealed off at 3!.

Of course it is to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. For example, the invention can be applied to tubes of other types in which other numbers of grids might b used. Various other changes embodying cathode, and insulation interposed between said resilient conductor and said filamentary cathode.

2. An electrical space discharge tube comprising a filamentary cathode, an anode, means supporting said cathode and anod relative to each other, a tongue formed on said anode by a U slot therein, a. resilient conductor secured to said tongue and-resiliently engaging said filamentary cathode for substantially inhibiting vibration of saidfilamentary cathode, and insulation interposed between said resilient conductor and said 2 filamentary cathode.

PERCY L. SPENCER. 

